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Paper: VSOP’s Legacy for Our Understanding of Magnetic Fields in Active Galactic Nuclei
Volume: 402, Approaching Micro-Arcsecond Resolution with VSOP-2: Astrophysics and Technologies
Page: 236
Authors: Gabuzda, D.C.
Abstract: Although relatively few polarisation-sensitive observations were carried out with VSOP, they have had a profound effect on our picture of the compact central regions of radio emission in Active Galactic Nuclei (AGN). The extra resolution provided by these images at relatively low frequencies provided new information about the “core” polarisation observed in ground-based images, indicating that this polarised emission is, in many cases, associated with newly emerging jet components, rather than the intrinsically optically thick core. A joint analysis of VSOP and VLBA polarisation observations near in time revealed the first observation of the theoretically predicted 90-degree rotation in polarisation angle associated with the transition from the optically thick to the optically thin regime. Perhaps most significantly, and quite unforeseen, VSOP polarisation observations provided the first clear evidence that at least some of the polarisation associated with the jets of AGN is associated with the “intrinsic” magnetic fields of the jets themselves, rather than local phenomena, such as shock compression or shear interaction with the surrounding medium. These extremely important VSOP polarisation observations have had a profound influence on subsequent work in this field, leading to a whole new series of VLBI studies focusing on the possibility that many AGN jets may have helical magnetic fields - which could come about naturally via the combined effect of the rotation of the central supermassive black hole and accretion disk and the jet outflow. These studies, in turn, provide crucial new links with theoretical investigations and concepts, making it possible for VLBI observations to seriously address for the first time such fundamental questions as the launching and collimation mechanisms for the jets. Key VSOP polarisation observations and the fundamentally new studies to which they have led are reviewed.
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